APPLICATIONS

Background: CAD is essential for the de novo synthesis of pyrimidine nucleotides and possesses the following enzymatic activities: glutamine amidotransferase, carbamoyl-phosphate synthetase, aspartate transcarbamoylase, and dihydroorotase. Thus, the enzyme converts glutamine to uridine monophosphate, a common precursor of all pyrimidine bases, and it is necessary for nucleic acid synthesis (1). In resting cells, CAD is localized mainly in the cytoplasm where it carries out pyrimidine synthesis. As proliferating cells enter S phase, MAP Kinase (Erk1/2) phosphorlyates CAD at Thr456, resulting in CAD translocation to the nucleus. As cells exit S phase, CAD is dephosphorylated at Thr456 and phosphorylated at Ser1406 by PKA, returning the pathway to basal activity (2). Various research studies have shown increased expression of CAD in several types of cancer, prompting the development of pharmacological inhibitors such as PALA. Further studies have identified CAD as a potential predictive early marker of prostate cancer relapse (3).

APPLICATIONS

Background: Glutamate dehydrogenase is a mitochondrial enzyme that catalyzes the oxidative deamination of glutamate to α-ketoglutarate through association with the cofactor nicotinamide adenine dinucleotide phosphate (1). Glutamate dehydrogenase is highly expressed in various tissues such as the liver, brain, kidney, heart, pancreas, ovaries, and testis. Two isoforms produced by two distinct genes are found in mammalian tissues. The GLUD1 gene is ubiquitously expressed (2), while the GLUD2 gene is specifically expressed in testicular tissues and astrocytes (3,4). Glutamate dehydrogenase links glutamate to the Krebs cycle, thereby playing a critical role in the regulation of energy homeostasis. Research studies have shown that changes in glutamate dehydrogenase activity in pancreatic β-cells can cause a hyperinsulinism syndrome (5).

APPLICATIONS

Background: Methyl-CpG-binding protein 2 (MeCP2) is the founding member of a family of methyl-CpG-binding domain (MBD) proteins that also includes MBD1, MBD2, MBD3, MBD4, MBD5 and MBD6 (1-3). Apart from MBD3, these proteins bind methylated cytosine residues in the context of the di-nucleotide 5´-CG-3´ to establish and maintain regions of transcriptionally inactive chromatin by recruiting a variety of co-repressor proteins (2). MeCP2 recruits histone deacetylases HDAC1 and HDAC2, and the DNA methyltransferase DNMT1 (4-6). MBD1 couples transcriptional silencing to DNA replication and interacts with the histone methyltransferases ESET and SUV39H1 (7,8). MBD2 and MBD3 co-purify as part of the NuRD (nucleosome remodeling and histone de-acetylation) co-repressor complex, which contains the chromatin remodeling ATPase Mi-2, HDAC1 and HDAC2 (9,10). MBD5 and MBD6 have recently been identified and little is known regarding their protein interactions. MBD proteins are associated with cancer and other diseases; MBD4 is best characterized for its role in DNA repair and MBD2 has been linked to intestinal cancer (11,12). Mutations in the MeCP2 gene cause the neurologic developmental disorder Rett Syndrome (13). MeCP2 protein levels are high in neurons, where it plays a critical role in multiple synaptic processes (14). In response to various physiological stimuli, MeCP2 is phosphorylated on Ser421 and regulates the expression of genes controlling dendritic patterning and spine morphogenesis (14). Disruption of this process in individuals with altered MeCP2 may cause the pathological changes seen in Rett Syndrome.

APPLICATIONS

Background: Mammalian cells synthesize serine de novo by diverting a portion of the glycolytic intermediate 3-phosphoglycerate into the phosphorylated pathway of serine synthesis. This shift supports anabolism by providing precursors for the biosynthesis of proteins, nucleotides, creatine, porphyrins, phospholipids, and glutathione. Phosphoglycerate dehydrogenase (PHGDH) catalyzes the first step in the serine biosynthesis pathway by converting 3-phosphoglycerate into phosphohydroxy pyruvate (1).Research studies demonstrate that an increase in serine biosynthesis supports growth and proliferation of cancer cells (2-4), which is supported by amplification and overexpression of PHGDH in a subset of melanoma and breast cancers (5,6). Suppression of PHGDH expression in cell lines with elevated PHGDH levels causes a strong decrease in cell proliferation and inhibits tumor growth in vivo (5). Additional evidence suggests that PHGDH interacts with and stabilizes FoxM1, which promotes the proliferation, invasion, and tumorigenicity of glioma cells (7).